In a semiconductor device which drives a load by using a power transistor, there is a case where a detection function is implemented to detect the state of the load. As the detection of the state of the load, the detection of a load extraordinary state is exemplified (such as over-current, a light load state (a disconnected state of a part of the load), no load state (a fully disconnected state of the load), and the detection of the load current which flows through the load.
Various techniques are proposed to detect a load current precisely. For example, Patent Literature 1 (JP H10-116917A) discloses a technique of detecting the output current of a planar-type bipolar transistor. This Patent Literature discloses a structure that an electrode is provided in an exposed collector layer on the surface of a transistor chip to take out a voltage drop due to the resistance of a silicon substrate as a current detection signal.
Also, the current according to the output transistor provides a transistor for the flowing sense and Patent Literature 2 (JP 2011-166518A) discloses a technique that a current which flows through a sense transistor according to an output transistor is detected as a voltage drop due to a sense resistance.
Moreover, Patent Literature 3 (JP H08-102649A) discloses a technique that a current which flows through a sense MOS transistor according to a power MOS transistor used as an output transistor is detected by a current detecting circuit which is connected with a source of the sense MOS transistor. In the technique disclosed in the Patent Literature 3, a source-drain voltage of the power MOS transistor and a source-gate voltage of the sense MOS transistor are adjusted to be same by a voltage source connected between the source of the power MOS transistor and the minimum voltage point of the current detecting circuit.